Well, Mr. Gilson is right, BUT...there's more to it, of course. A lead acid battery is good in automobile service 4-5 years max. This is with regular use and no abuse. At three years old and evidence of weakness, a good (larger) battery may be in order. You would do well to check the voltages, engine off, and running and also with all electrics on and running.Could be as simple as needing to tighten the alternator's tension on the belt a bit. The alternator may be getting tired, too. Voltage checks will help pin-point the REAL problem. (You'll find in my posts a lot of references to the REAL problem!.. this is where REAL fixes originate)